The present disclosure relates to a method and an apparatus for switching on a voltage supply of a semiconductor circuit and to a correspondingly configured semiconductor circuit.
The switching off of unrequired circuit blocks of a semiconductor circuit is a proven method of reducing leakage current losses in intermittently unrequired circuit portions. Once they have been switched off, the inner capacitors of the switched off circuit blocks discharge. These capacitors have to be recharged once they have been switched on again. Uncontrolled switching operations (glitches) can occur during the reconnection process and cause additional current on supply lines of the semiconductor circuit in addition to the load current for the capacitors. Consequently, a high current peak has to be allowed for shortly after a circuit block has been switched on again. This causes a high IR drop (a drop in the supply voltage due to resistive influences), which temporarily reduces the supply voltage of circuit portions adjoining the voltage blocks which have just been switched on and can thus lead to violation of the timing behavior and to disturbances in operation in these circuit portions, also known as soft error. For this reason, it is of crucial importance to monitor and minimize the current peak when switching on circuit blocks which are intermittently switched off.
In addition to the circuit peaks caused by the resistive drop in voltage, the rise rate, at which the load current rises, also leads to problems when the voltage supply is switched on. This effect is due to the action of parasitic inductances, which, in accordance with:
  U  =      L    *                  ⅆ        l                    ⅆ        t            also lead to a voltage drop in the supply voltage which is proportional to the rise rate.